const obj = { name: '哈哈' }
function fn() {
    console.log(this)
    return () => {
        console.log(this)
    }
}
const resFn = fn.call(obj) // { name: '哈哈' }
resFn() // { name: '哈哈' }

const obj2 = {
    name: '波仔',
    say: () => {
        console.log(this)
    }
}
obj2.say() // window